Actually once you get it loose, you can probably move around on the shock itself while turning the bolt with your fingers and get it on out without the 1/4 turn business. By moving the shock you can find a place where it is not putting any resistance on the bolt, letting it come out with your fingers.

Those are the kinds of things that you learn after a few years of wrenching.

If you grind down a wrench, don't expect that wrench to be accepted under warranty by ANY toolmaker. If you were to grind down a cheap wrench then it may not be strong enough to take it. Even some of the sources that sell semi cheap tools should have something thin enough to fit in there. Craftsman wrenches have been bulky since about 1970 or so. Before that time Craftsman open ends were known to spread when torqued hard. At that point they beefed them up so that they would not spread as bad, but in the process started making wrenches that you couldn't fit in a tight spot.

It COULD be that the Craftsman POLISHED combinations might be made thin like the other makers.

Good luck,